1. Field Of The Invention
The present invention is directed to subsea drilling operations and, in certain particular embodiments, to retrieval systems and operations for retrieving pod containers from a subsea lower marine riser package platform.
2. Description of Related Art
In subsea drilling operations, one or more subsea pod containers are located on a lower marine riser package (xe2x80x9cLMRPxe2x80x9d) platform encompassing a riser through which drilling operations are conducted. These xe2x80x9cpodsxe2x80x9d contain electronics and valves that are used in the monitoring and control of a wide variety of functions related to drilling operations. Typically the pods are releasably connected to an LMRP which is the top portion of a structure or xe2x80x9cstackxe2x80x9d that includes blowout preventers (xe2x80x9cBOPxe2x80x9d) and related apparatus used for well control.
The prior art discloses redundant systems which employ two similar pods so that if there is a failure in one xe2x80x9con linexe2x80x9d pod, e.g. a failure of electronics or of a valve, the other xe2x80x9cstandbyxe2x80x9d pod can be brought to an xe2x80x9con linexe2x80x9d status, e.g. by a Driller, to immediately perform the required actions or functions. The retrieval of a pod for replacement or for repair is a complex and expensive operation. To retrieve an LMRP with a failed pod requires removal of the riser to which the LMRP is connected. The riser extends from the drill floor, e.g. from a boat or rig at the water""s surface, down to the stack. xe2x80x9cTrippingxe2x80x9d out the riser is a long expensive process, and LMRP retrieval requires such a xe2x80x9ctrip.xe2x80x9d
Many prior art deep water multiplexed BOP Control Systems include two identical systems either of which may control Stack functions. One such system is illustrated schematically in FIG. 1. This configuration is commonly referred to as being xe2x80x9cDually Redundantxe2x80x9d. Both systems may be active electronically and may have single or dually redundant sets of electronic controls. One of the systems including one of the pods is active hydraulically. The system that is active hydraulically is manually selected by a Driller to be the active system or xe2x80x9cActive Podxe2x80x9d. Each system, or Pod, is equipped with an hydraulic conduit supply. This supply is run from an Hydraulic Pressure Unit (HPU) on the surface to the Pod that is mounted on the LMRP. A xe2x80x9cCrossover Valvexe2x80x9d may be actuated. This actuation diverts hydraulic fluid from the Pod it is designed to supply to the redundant Pod normally supplied by the other conduit. This xe2x80x9cCrossoverxe2x80x9d function allows either Pod to be supplied by either conduit. This is a Driller actuated, manual function and pod redundancy is lost during retrieval.
Also mounted on the LMRP are Hydraulic Accumulators. These Accumulators supply hydraulic fluid for the Stack functions at a consistent pressure so that a function is actuated according to the manufacturer""s specifications. Each Pod""s Hydraulic supply conduit is connected to the Hydraulic Accumulator""s Hydraulic Manifold so that the conduit which has been selected as the active Hydraulic supply line may xe2x80x9cchargexe2x80x9d the Hydraulic Accumulators. Check valves prohibit the hydraulic fluid from backing-up the un-used, or not active, Hydraulic supply conduit. Thus, whichever conduit is selected as the active hydraulic supply will xe2x80x9cchargexe2x80x9d the LMRP mounted Accumulators. API requirements as well as normal xe2x80x9cOil-Field traditionxe2x80x9d classify one of the hydraulic supply conduits as the Blue supply. The other hydraulic supply conduit is classified as the Yellow supply. The Pod traditionally associated with the Blue supply is classified as the Blue Electro/Hydraulic (E/H) Pod, or Blue Pod. Conversely, the other Pod is traditionally classified as the Yellow Pod (e.g. as shown in FIG. 2).
Any failure that causes a loss of the dual redundancy can result in the retrieval of the LMRP. This could be a failure in the electronics; a failure in a solenoid valve; a failure in a pilot device, i.e. a pressure switch or analog device; a failure of a piloted device, i.e. a Sub-plate Mounted (xe2x80x9cSPMxe2x80x9d) hydraulically actuated valve; or a failure in a check or shuttle valve. It could also be a failure in the hydraulic piping or in the electrical wiring. In any case, a choice to pull the LMRP can be made. In the direct hydraulic shallow water systems, the Pods are normally retrieved via guidelines if a failure has occurred. In deep water this has not been the case. In the shallow water systems it should be noted that even though the Pods may be retrieved, drilling is normally terminated until the Pod has been pulled, corrected, and re-deployed.
A typical prior art Blowout Preventer (BOP) Control System regulates a well during drilling operations and continuously monitors the status of such operations. The BOP system includes a structure that incorporates hydraulically actuated well control safety devices and their peripheral components, i.e. blowout preventer system. Such apparatus is referred to as the Blow Out Preventer Stack or simply as the xe2x80x9cStackxe2x80x9d. The upper portion of the xe2x80x9cStackxe2x80x9d is referred to as the Lower Marine Riser Package (LMRP). The LMRP includes a platform and is the interface between the Riser system and the xe2x80x9cStackxe2x80x9d. It is a separate structure and is supplied with, or as a part of, the xe2x80x9cStackxe2x80x9d. The LMRP is connected to the xe2x80x9cStackxe2x80x9d via a hydraulically actuated xe2x80x9cStackxe2x80x9d connector. It is connected to the Riser by a xe2x80x9cRISERxe2x80x9d connector. Between these two connections there may be inserted xe2x80x9cBAGxe2x80x9d BOP""s xe2x80x9cPipexe2x80x9d BOP""s (Pipe Rams), and/or other instrumentation or controlled protective and supplementary equipment. This LMRP xe2x80x9cplatformxe2x80x9d also physically supports hydraulic accumulators and the BOP Control System Subsea Electro-Hydraulic (E/H) xe2x80x9cPODSxe2x80x9d. These subsea xe2x80x9cE/H Podsxe2x80x9d perform the well control regulation tasks as supervised by the Driller from the Drill Floor of the Rig. The Driller may regulate a parameter, i.e. a hydraulic pressure subsea on the LMRP or xe2x80x9cSTACKxe2x80x9d, or control a function, i.e. close a pipe ram BOP, and/or monitor the real time actuation of the function controlled or the parameter regulated.
Many of the BOP Control System""s end functions are on the lower portion of the xe2x80x9cSTACKxe2x80x9d, i.e. below the LMRP xe2x80x9cSTACKxe2x80x9d Connector. A command from the Driller is transmitted serially via fiber optics or cable, onto a xe2x80x9cdata freewayxe2x80x9d. The electronic I/O equipment located in the Subsea E/H Pod retrieves data and instructions from, and writes status to, the data freeway. These instructions (commands) are performed with electronic I/O equipment that interfaces with electro/hydraulic functions, i.e. electrical solenoid valves. These solenoid valves either hydraulically actuate LMRP functions directly, or pilot larger valves i.e., sub plate mounted (SPM) valves. These SPM valves supply hydraulic fluid at greater volumes or flow rates than could be accomplished with the solenoid valves themselves.
These SPM valves supply hydraulic fluid to hydraulic connectors, or stab plates, which allow LMRP accumulator hydraulic fluid flow to the xe2x80x9cStackxe2x80x9d mounted functions below. The LMRP Accumulators are supplied via multiple sources from the surface Hydraulic Pressure Unit (HPU). The LMRP Accumulators are xe2x80x9cfloatxe2x80x9d charged by the Driller selected surface hydraulic source, i.e. one of the multiple sources. This fluid, in route to a Stack mounted function, migrates through the solenoid valve, to the SPM valve piloted actuator, through the SPM valve supply ports, through the hydraulic connector, through a series of shuttle and check valves, and then on to actuate the desired Stack mounted, piston-like, function. These Stack mounted functions are referred to as a xe2x80x9cStack functionxe2x80x9d. The series of shuttle and check valves encountered by the hydraulic flow is necessary to enable redundancy of control. There is an E/H Pod associated with each of the surface hydraulic supplies.
As stated above for redundancy, xe2x80x9cOil Fieldxe2x80x9d tradition dictates that one hydraulic source be associated with one E/H Pod. This Pod will be designated as the xe2x80x9cBlue Podxe2x80x9d. Another hydraulic source will be associated with another EH Pod and this combination should be labeled the xe2x80x9cYellow Podxe2x80x9d. Each one of these pods are identical, and contain identical components, i.e. the electronic I/O, the solenoid valves, the SPM valves, and the hydraulic stab plate (LMRP side). Each hydraulic stab plate, xe2x80x9cStack-sidexe2x80x9d, is connected by hydraulic tubing to the shuttle/check valve tubing and so terminated at the end function (Not Redundant). Only one pod is hydraulically active at a time. The other pod is considered a hot back up and may be electrically active and functioning. The electronic I/O (Input/Output) and the solenoid valves portion of the E/H Pod are referred to as the Subsea Remote Terminal Unit (SSRTU). In one integrated prior art system, the Driller is supplied with two panels. These panels mimic a portion of the BOP Control System. One panel will mimic the Blue E/H Pod. The other panel mimics the Yellow E/H Pod. Primary control of the BOP system is provided through panel mounted Push Buttons. Panel display of the system status is via lighted Push Buttons and/or pilot lights. Analog values are displayed via Analog/Digital meters. The operation of any SSRTU function begins animation with the depression of an associated Push Button. For critical functions, the Push Button must be depressed while simultaneously depressing the xe2x80x9cpush and hold-ARMxe2x80x9d Push Button. These Push Button depressions must be conducted on the panel, Blue or Yellow., depending on which panel is hydraulically active. It is a Driller function to select one of the hydraulic subsea sources as active, i.e. either the Blue Hydraulic line or the Yellow hydraulic line. Logically, the Push Button Depression is conducted on the Pod whose hydraulic line is active, i.e. the one charging the LMRP accumulators. Identical control activity can also be performed in like manner from the Blue or Yellow Toolpusher""s Panel. Two Personal Computers each with an MMI (xe2x80x9cman-machinexe2x80x9d) interface may be provided, one in the Driller""s House and the other in the Toolpusher""s office. It is possible with some prior art systems to use the MMI""s instead of the panels for primary control of the SSRTU""s.
In one such prior art system in which the Driller has two panels and the Toolpusher has two panels (total of four panels), command data may be sent from any panel or from dual MMI interfaces to a surface mounted Programmable Logic Controller (PLC), usually in a dually redundant mode. The surface PLC may also be referred to as a central control unit or central computer unit (CCU). The CCU processes commands through audible or optical modems and transmits them to the SSRTU""s. These SSRTU""s are either PLC devices or microprocessor printed circuit boards and each SSRTU may be referred to as a controller. Each controller has associated electrical I/O units. These controllers are enclosed in pod containers (also referred to as electronic pods). The SSRTU""s mounted on the LMRP, one of which is the on-line unit, executes the command received from the modems. xe2x80x9cInferredxe2x80x9d position sensors, pressure xe2x80x9cfeed backs,xe2x80x9d transmit a signal indicating a command has been executed back to the CCU and the originating panel, or MMI via modem transmissions. Activation of a pilot light or a flow meter readback confirms the execution of the commanded function at all panels and at the MMI""s. CCU functions are performed sequentially via serial data links to the remote I/O either in the panels or in the SSRTU""s. If a function is not accomplished, the Driller is alerted to this and can change the system configuration to put an alternate pod on-line. If, e.g. the Driller is working on the Blue Pod fed from the Blue hydraulic conduit, he first changes to the Yellow hydraulic conduit and again tries to accomplish the previously-commanded function. If this does not work the Driller transfers control to the Yellow pod operating off of the Yellow hydraulic conduit. If the commanded function still is not accomplished, the Driller reconfigures the system with the Yellow pod using the Blue hydraulic conduit. If the command is not accomplished, typically the entire LMRP is tripped out to discover and correct the problem.
There has long been a need, recognized by the present inventor, for a safe, relatively inexpensive, and simple pod retrieval system and method. There has long been a need for such a system and method which does not require tripping of the riser to effect removal of a pod. There has long been a need for such a system and method with which drilling need not be terminated while accomplishing pod retrieval. There has long been a need for a multiply redundant stack control system.
The present invention, in certain aspects, provides a method and a system for the efficient and effective retrieval of a pod container from a lower marine riser package platform on a subsea stack without removal of the platform from the stack, without tripping the riser, and while drilling operations continue without interruption. Preferably with such methods and systems no unwanted forces, e.g. but not limited to lateral forces, are applied to the riser or to other items.
In certain embodiments of the present invention, a remotely-operated retrieval module is moved to a position above a subsea pod to be retrieved. One or more lines are connected between the retrieval module and the platform for stability during the operation. In one aspect, the line is connected by a remotely operated vehicle. A pod holder is then released from the retrieval module to descend down around the pod. The pod holder is secured to the pod; the pod is released from the platform; and then the pod holder rises (e.g., ballasted by air) to re-unite with the retrieval module. Following disconnection of the line or lines securing the retrieval module to the platform, the retrieval module is raised to the surface and the pod is removed therefrom. A pod may be releasably secured to a lower marine riser platform with any suitable known device or mechanism, including but not limited to, those disclosed in U.S. Pat. No. 5,398,761 and the prior art cited therein, all of which is incorporated fully herein for all purposes.
In one particular system according to the present invention, a lower marine riser package platform with three pod containers provides a multiply redundant system in which any one of the three pods can perform required functions. Of course it is within the scope of this invention to use four, five or more pod containers to achieve multiple redundance.
The present invention, in certain embodiments, uses components as in various prior art systems. In one embodiment no CCU is used. Due to the critical nature of these control systems, additional components may be included in certain embodiments according to the present invention to provide a series of xe2x80x9cstand alonexe2x80x9d system which insures a more reliable, therefore safer, and more economic, BOP control system thus lowering drilling costs.
Certain preferred embodiments according to the present invention do not use the prior art sequential logic prevalent in industrial PLC""S (no CCU) and do not rely upon a personal computer (PC) networking of distributed I/O which is also a feature of many prior art systems. In certain embodiments according to the present invention, two communication protocols are utilized, ARCNET (trademark) communication system and ETHERNET (trademark) communication system, to arrange a network of computers, controllers, and field mounted devices into a fieldbus (as is commonly used in the industrial automation industry). This fieldbus delivers messages in a time predictable fashion. ARCNET (trademark) communication system provides for the successful transmission and reception of a data packet between two network nodes. A node refers to an ARCNET (trademark) communication system controller chip and a cable transceiver connected to the network. Nodes are assigned addresses and one ARCNET (trademark) communication system network can, in certain aspects, have up to 255 uniquely assigned nodes. To each ARCNET (trademark) communication system node in the proposed system a 32 bit microprocessor controller with up to 4 MB of battery-backed memory and 2 MB of Flash EEPRom is incorporated. Each of these nodes is referred to as a xe2x80x9ccontroller.xe2x80x9d
In one aspect a BOP Control System according to the present invention has a Blue and Yellow Driller""s Panel and a Blue and Yellow Toolpusher""s Panel. In the present invention, there is a Blue controller and a Yellow controller for the Driller""s Panel and Blue Controller and a Yellow controller for the Toolpusher""s Panel. The network communicates with each node (controller) through a multi-drop Ethernet Hub. On the surface there are dual ETHERNET (trademark) communication system Hubs for reliability""s sake. In certain aspects there are two PC""s and each PC is configured as an ARCNET (trademark) communication system Node (or controller) equipped with MMI (Man Machine Interface) capability. These PC nodes are also multi-dropped from each of the two ETHERNET (trademark) communication system Hubs. Each of these MMI""s may operate as a xe2x80x9csoftxe2x80x9d Driller"" Panel or a xe2x80x9csoftxe2x80x9d Toolpusher""s Panel. (xe2x80x9cSoftxe2x80x9d means software controlled rather than hardware controlled.) The PC""s have the ability to upload each controller""s memory for dataxe2x80x94logging, trending and reduction and can also be used to download executable programs into the controllers if one""s program becomes corrupt.
With ARCNET (trademark) communication system""s xe2x80x9ctoken passingxe2x80x9d protocol, communication between nodes takes place in ascending order, i.e. first node (lowest address) to second node (next highest address) and so on. The network automatically reconfigures itself if another node is added or if a node fails to respond (based upon number of failures/unit of time). Should a node fail to respond, the node is bypassed (and alarmed) to the next node. Therefore, there is no xe2x80x9chang-upxe2x80x9d in the network.
Communication from the controller to the I/O is the subhierarchy. Each controller is also equipped with an ETHERNET (trademark) communication system chip which allows the controller to interface with an ETHERNET (trademark) communication system hub which polls each SMART I/O) (Brain Boards) in the same multi-drop fashion that occurs on the ARCNET (trademark) communication system side of the digital network. Each brain board communicates with its associated I/O and supplies discrete change anti-coincident circuitry, means, maximums, minimums, standard deviations, sums, and flags upon exceeding upper or lower limits. The brain board also toggles, latches, unlatches, or times the digital discrete status as so directed by its controller.
Once a program (or strategy) has been downloaded into a pod""s controller""s memory and the controller and its associated I/O have been xe2x80x9cpowered-up,xe2x80x9d the controller runs its program continuously. It is totally independent of any other controller and it is also independent of the network even though it is a component part of the network. Any of the controllers on the surface, i.e. the Driller""s MMI, his Blue Panel, his Yellow Panel, the Toolpusher""s MMI, his Blue Panel, or his Yellow Panel, can issue a command to any one of the SSRTU""s. In one aspect the additional SSRTU is used and is identified as the xe2x80x9cPurplexe2x80x9d SSRTU. In such a system there are a Blue SSRTU, a Yellow SSRTU, and a Purple SSRTU. Each SSRTU (Controller) is interfaced to each surface ARCNET (trademark) communication system Hub through fiber optic cable. For expediency""s sake, the surface ARCNET (trademark) communication system nodes may probably interface to the hubs via fiber optic cable. All ETHERNET (trademark) communication system connections to the ETHERNET (trademark) communication system Hubs may be via coax cable or twisted shielded pairs of conductors. Each controller has dual communication lines, one from each ARCNET (trademark) communication system Hub.
In certain embodiments with three SSRTU""s, there are three hydraulic conduit lines (see e.g. FIG. 19). In one aspect the valves are arranged so that each of the SSRTU""s may be supplied from any of the three hydraulic supply lines.
The three SSRTU""s may be configured by the Driller in one of the three ways listed below (see e.g. FIGS. 18 and 20):
1. Blue SSRTU as Master
Yellow SSRTU as Standby
Purple SSRTU as Marshal
2. Yellow SSRTU as Master
Purple SSRTU as Standby
Blue SSRTU as Marshal
3. Purple SSRTU as Master
Blue SSRTU as Standby
Yellow SSRTU as Marshal
The Master unit (or pod) or the Standby unit can pilot a function (e.g. operate an SPM valve) by energizing either a coil of a dual coil solenoid valve in the Master Unit Solenoid Valve can. This energizing of a coil by the Master or Standby electronics is referred to as being xe2x80x9cfired byxe2x80x9d either the Master or Standby electronics in the Master Electronics pod container. It should also be noted that the Master unit in FIG. 18 supplied by conduit A is fired by Power Transformer A. The coil energized by the Standby Unit is fired by Power Transformer B. One catastrophic failure would be a failure of a controller or a Power Transformer. The failure of a controller would essentially be the same as a failure of communications to the controller. With such a failure, the Driller reconfigures the system so that the failed unit (controller or Power Transformer) is assigned to the Marshal Unit and then insure that the Marshal Unit is placed out of service. This would leave the BOP Control System with two good pods with each pod being dually redundant as well as the two pods offering dual redundancy. In this configuration, drilling would continue uninterrupted. The failed pod is retrieved as disclosed herein for repair, and the repaired pod is re-deployed to the LMRP, preferably without putting any lateral force on the Riser, the LMRP, or the Stack and without interrupting drilling operations.
It is, therefore, an object of at least certain preferred embodiments of the present invention to provide:
New, useful, unique, efficient, nonobvious systems and methods for the retrieval of pod containers used in subsea drilling operations;
Such a system and method which do not require the separation of a lower marine riser platform from a subsea stack or the tripping of a riser to retrieve a pod container;
Such methods and systems which permit pod retrieval without the interruption of drilling operations; and
Such a system with three or more pod containers, each pod container with dually redundant electronics, providing multiple redundancy of function.
Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures and functions. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims to this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that the conceptions of this disclosure may be used as a creative basis for designing other structures, methods and systems for carrying out and practicing the present invention. The claims of this invention are to be read to include any legally equivalent devices or methods which do not depart from the spirit and scope of the present invention.
The present invention recognizes and addresses the previously-mentioned problems and long-felt needs and provides a solution to those problems and a satisfactory meeting of those needs in its various possible embodiments and equivalents thereof. To one skilled in this art who has the benefits of this invention""s realizations, teachings, disclosures, and suggestions, other purposes and advantages will be appreciated from the following description of preferred embodiments, given for the purpose of disclosure, when taken in conjunction with the accompanying drawings. The detail in these descriptions is not intended to thwart this patent""s object to claim this invention no matter how others may later disguise it by variations in form or additions of further improvements.